I've noted people make bold the vowels in stressed syllables. There is a simpler way, a special character that you put after a stressed vowel. It is shown by all the modern browsers correctly.
So here it is.
Приве́т из Сиби́ри!
It isn't standing alone in the text and there is some unusual behaviour when you try to highlight it, but you can copy it together with the 2 neibour letters:
и́р
and then del and backspace the и and р, and the sign will automtically jump to the preceding letter. It works both for editing textbox and for webpage rendering. My text editor, UltraEdit 9.10 also handles it correctly.